The library is really simple to use. Basically, include the script musical.js, and then:
piano = new Instrument('piano'); piano.play('ccggaag2');
Then with any WebAudio browser, you will be Baahing with the Black Sheep, Twinkling with the Stars, or singing your ABCs with me. The notation used is called ABC Notation, and it is used for a lot of simple sheet music online.
The library comes out of work from beefing up music support in Pencil Code. The WebAudio sequencer in that library has improved enough that it deserves to be a separate library.
You can also play with it as part of the turtle library on pencil code here: that example is a simple interactive piano keyboard where you can see the keys.
Have fun. Let me know if you encounter any problems, or if you have any ideas for improvements. Always looking for open-source contributions.